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Difficulty: MediumPopulation Dynamics and Ecological Sampling

During a field study of an intertidal mangrove swamp in Cross River State, a student used a 0.5 m×0.5 m0.5\text{ m} \times 0.5\text{ m} quadrat frame to sample the periwinkle (*Tympanotonus fuscatus*) population. Across 1010 randomly placed quadrat throws, a total count of 180180 periwinkles was recorded. What is the estimated population density of *Tympanotonus fuscatus* per square metre in this habitat?

  1. A
    18 periwinkles/m218\text{ periwinkles/m}^2
  2. B
    45 periwinkles/m245\text{ periwinkles/m}^2
  3. 72 periwinkles/m272\text{ periwinkles/m}^2Answer
  4. D
    720 periwinkles/m2720\text{ periwinkles/m}^2

Answer

The estimated population density is 72 periwinkles/m272\text{ periwinkles/m}^2.
The correct option correctly evaluates population density by calculating the total sampled area (10×0.25 m2=2.5 m210 \times 0.25\text{ m}^2 = 2.5\text{ m}^2) and dividing the total counted organisms (180180) by that area, yielding 72 periwinkles/m272\text{ periwinkles/m}^2.

Step-by-Step Solution

1
Calculate the area of a single quadrat frame
Area of 1 quadrat = 0.5 m×0.5 m=0.25 m20.5\text{ m} \times 0.5\text{ m} = 0.25\text{ m}^2.
Determines the surface area enclosed by one sampling unit.
2
Determine the total area sampled across all throws
Total sampled area = 10 throws×0.25 m2=2.5 m210 \text{ throws} \times 0.25\text{ m}^2 = 2.5\text{ m}^2.
Accounts for the cumulative ground area surveyed during the 10 quadrat throws.
3
Calculate the population density per square metre
Population density = Total number of organismsTotal sampled area=1802.5 m2=72 periwinkles/m2\frac{\text{Total number of organisms}}{\text{Total sampled area}} = \frac{180}{2.5\text{ m}^2} = 72\text{ periwinkles/m}^2.
Population density is expressed as the total number of individuals per unit area.

Key Concept

Quadrat Population Density Calculation
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Topics

Population Dynamics and Ecological Sampling

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